Beyond frustrated

[Spot]

Originally Posted by Mike Burch

8 ohms resistance is much too high. It sounds very much like a cable fault. In my experience, it's quicker and easier to pull a new wire through (using the old one as a puller) than to try and track down a cable fault—especially as the fault is always in the least accessible place!

60 ft 14 gauge copper at room temp 20 C s/b .152 ohms according to multiple calculators online. With a piece of known good 14 gauge one could try to isolate which leg has the high resistance.

[Sailor_Al]

What is switching the light? Is it a conventional light switch, or is it controlled by an electronic output of some controller; a solid state output. A soils state output will bleed amount current while OFF to drive the high impedance meter and not the led load.

[thomm225]

Originally Posted by fourlyons

Your digital multimeter, unlike an old school analog voltmeter, pulls nearly no current through the circuit. So it is easily "fooled" by a high resistance connection. Hook a 12 volt incandescent bulb or small electric motor to the circuit then read the voltage, it will be too low to run either.

Both the digital and analog meters will have very high impedance as compared to the circuit (especially the circuit in question) so that wouldn't be the problem when you hook up either to take a measurement.

All meters have high impedance so they don't load down the circuit when you hook them up in parallel. Very little current flows through them as compare to the circuit due to the high impedance.

It's probably the polarity as has been mentioned.

[skipmac]

Originally Posted by Mike Burch

In my experience, it's quicker and easier to pull a new wire through (using the old one as a puller) than to try and track down a cable fault—especially as the fault is always in the least accessible place!

Not on my boat. All the wires are run in bundles, through conduits and most of the bundles tie wrapped tightly. Pulling a wire through that is impossible. Ask me how I know.

[AndyEss]

Originally Posted by pas63

Wire up the light, nothing. I check the voltage, 12.7V, more than enough for an LED light. Polarity is correct, so I temporarily connect it straight to supply voltage and get light, so the light is good. Hook up the volt meter, 12.7V, lower than the panel (14.6v), but it is probably a 20-30' run over 14 ga wire. Turn the breaker off, check the VM, .1V. Turn the breaker back on and back to 12.7V. Reconnect the light, nothing. Where it gets really bizarre is I can short the pos and neg leads feeding the light and no firework or popped breaker which tells me I don't have voltage but the damn VM does show voltage

You are dropping nearly 2 volts (14.6 to 12.7) in that short run. This is way to much. Elsewhere in the thread you said you measured 8 ohms on one of the legs as its wire resistance - this is way too much. You have badly corroded wiring or connections on that circuit.
Run a new circuit or attach to the courtesy light circuit.

[pas63]

Thanks for all the info. As skipmac said, pulling out the old wire is all but impossible to pull out. I don't know what they were used for but I have quite a few dead wires I need to remove at some point.

Yesterday tracing wires out, I found a run to a long ago non-functing string of courtesy lights, with a splice that had to be done at the factory. The splice is right as it meets a bulkhead and the hull. I can only assume they did the same somewhere on the run for the light.

[Lake-Effect]

There are a number of ways to trace and check wiring - from a battery and a buzzer or light, ohmmeter, "fox and hound", to time-domain reflectometry. The better marine electrical books cover these.

If there isn't hidden wire damage, or a buried connection/splice (grrrr....) most connections are accessible. But if it's taking too long to locate a bad connection, it's often faster to just run new wire.

The wiring runs in most recreational boats isn't too horrible, and usually there's a logic to how the wires are run, and if you're lucky, there's some aids like strings in place for pulling wires through inaccessible runs. And having a fish wire/tape/rod is useful.

[pas63]

Lake-Effect, I've done my share of tracing bad wire, tracing it through bundles etc. This is a mid 80's boat and wile pretty decent over all, running wire through bilges is not my favorite. My electrical panel is over the stud settee. The wiring runs down the back of the settee, under and through a accessible hole into the bilge where they are all taped. In the end I might splice this 1 light into the courtesy light. I still need to pull as much dead wiring as possible that I can get any wiring through that almost inaccessible hole.

[sailorboy1]

didn't read all the thread, but

Even a bad wire should have same voltage at the end as the start under no load

Sometimes a new LED bulb just wouldn't work in an old receptacle even if it all tests out separate

[Lake-Effect]

Originally Posted by pas63

Lake-Effect, I've done my share of tracing bad wire, tracing it through bundles etc. This is a mid 80's boat and wile pretty decent over all, running wire through bilges is not my favorite. My electrical panel is over the stud settee. The wiring runs down the back of the settee, under and through a accessible hole into the bilge where they are all taped. In the end I might splice this 1 light into the courtesy light. I still need to pull as much dead wiring as possible that I can get any wiring through that almost inaccessible hole.

Understood. I hear you. Which is you want only dependable, splice-free, protected cables run down there, so you don't have to deal with that run very often.

But as long as tapping into the courtesy light circuit doesn't overload anything or compromise its operation, that's not a bad option.

[Rob19321]

I'm with one response above, disagree with LED using many amps.
LED base can light up with 0.6 v dc and milli-amps (That's 1 / 1000 amp).

One possible problem is polarity, and I know that you said it was right... but once things don't make sense, its time to respond with things that don't make sense.

LED are one direction so checking the directly at a source says the LED is good, doesn't get us to "polarity where installed is right."

[wing15601]

“Both ends are freshly terminated and no corrosion.”. You may also want to recheck those newly crimped terminals.

[djdeakyne]

You must measure the voltage at the light with it connected in the circuit.


Anything else tells you nothing.


If you truly have 12.7v at the light with the light connected, it will work, provided the polarity is correct. I suspect you don't really have 12.7v under load.

[Kolchac]

From my professional opinion you should:
1. make sure your LED lamp is 12V DC, not 120/240.
2. You cannot use an ohmmeter to test LED lamp. Connect the lamp directly to a battery 12 V, use fuse 10A 12V or 1A 120V (you can buy a wire with a fuse). That helps you to locate a problem - wire or lamp.
3. Change polarity - you will not damage anything.
4. The voltage drop from 14 to 12 is too much!

General knowledge: LED lamp is a matrix of LED diodes. To open a diode you need to apply 0.8 - 1.5 V. + to anode. So in a 12V lamp we have ~ serial connected 10-15 LEDs.

Do not change order of the steps above.
Good luck

[Lake-Effect]

Originally Posted by Rob19321

LED base can light up with 0.6 v dc and milli-amps (That's 1 / 1000 amp).

Small correction: silicon diodes and rectifiers will conduct at a forward voltage of around 0.6V. The semiconductors used in a LED won't conduct (and light) til the forward voltage is about 1.6v or higher, depending on the LED colour.